Method and device for switching over in a memory for a control device

ABSTRACT

A method and device for switching over in a memory for a control device, a first storage area in the control unit being overlaid by a second storage area; the second storage area including at least one memory page, and each of the memory pages being able to overlay the first storage area; switching over being able to be performed between the memory pages and the overlaying being able to be switched on/switched off, and the switching over of the memory pages and the switching on/switching off of the overlaying of the second storage area being automatically carried out and/or triggered by the software of the control unit.

FIELD OF THE INVENTION

The present invention relates to a method and a device for switchingover in a memory for a control device, e.g., a first storage area in thecontrol unit being overlaid by a second storage area. The presentinvention also relates to a computer program having program code,particularly stored on a computer-readable data carrier.

BACKGROUND INFORMATION

In control units, particularly in a motor vehicle, an existing memory,particularly a read-only memory is replaced or faded out in orderthereby to be able to adjust values or make settings while the controlunit is in operation. Besides motor vehicle control units, other controlunits are also conceivable in this context, such as aviation units oreven machine tools and machining centers, control units of automationtechnology, etc.

Such an emulation device for a control unit is described in GermanPublished Patent Application No. 39 17 979, a data manipulating devicebeing provided and an external and, particularly, a serial interface ofthe operator unit of the control unit for changing data of a read-writememory that is contained in the control unit. A switching device isprovided for switching the read access in the data manipulation device,which switches over, on the one hand, between the read-write memory, andon the other hand a data program read memory.

In the same vein, German Published Patent Application No. 41 07 052describes a device for the application of control units in which,likewise, the data/program read memory of the control unit is replacedby a data manipulation device having a read-write memory, to whichlikewise an operator unit is connected via a serial interface. Here too,a switching device is provided in which the read-write memory isconnected in a first cycle to the control unit for reading out data, andin a second cycle to the serial interface for reading in or reading outdata.

The switching over between the memories is performed by the connectedapplication unit, in this instance. In some microcontrollers, theoverlaying memory is made up of several regions, in this context, whichare able to be activated only region by region. In the process, it isfrequently not preventable that the control unit program accessesinconsistent data during the switching over between the regions. This isconditioned upon the fact that, because of the successive switching inof the regions, an intermediate reading comes about, with regard to theoverlaid storage area, during the switching over process which does notcorrespond to the desired final state of the data. Thus, the controlunit program accesses data which in part are made up of various storageareas and various regions. Because of this overlapping, what may happenis that the control unit software makes calculations using wrong data,which may lead to a corrupted result, and in the worst case even to aprogram crash.

Thus, conventional arrangements have not been able to yield optimumresults in all regards.

SUMMARY

Therefore, example embodiments of the present invention address thissituation, and provide a method and a device for switching over in amemory for a control unit, in which the mentioned data inconsistenciesare able to be avoided.

Example embodiments of the present invention provide a method and adevice for switching over in a memory for a control unit, a firststorage area in the control unit being overlaid by a second storagearea; the second storage area including one or more recording surfaces,and, e.g., each of the recording surfaces being able to overlay thefirst storage area; switching over being able to be performed betweenthe recording surfaces and/or the overlaying being able to be switchedon or off (EA), and the switching over of the recording surfaces of thesecond storage area being automatically carried out by the software ofthe control device. That is, for reasons of security, there is a secondrecording surface or the original store-and-forward mode is used as thedefault mode, in order to return the system controlled by the controlunit to a more secure state, if necessary, specifically by switchingover to another recording surface or by terminating the overlaying ofthe storage area, so as to unhide the original data again. According toexample embodiments of the present invention, the switching over of thesurfaces and the fading out of the storage area are performed by thecontrol unit software, in this instance. Because the control unitsoftware triggers and/or executes the switching over and the fading outof the storage area, it may be ensured that no access to inconsistentdata takes place, since no third entity is able to generate datainconsistencies by switchover triggering. In general usage, the fadingout of the storage area by a recording surface is also called pageswitching, since this procedure is similar to switching over between twomemory pages, one having the same content as the area that is to befaded out. Therefore, in the following the fading out of the storagearea by a page is designated as switching the page.

The switching over of the memory pages may be called for by theapplications system, namely, expediently such that the applicationssystem calls for the switching over by writing a switching identifierinto a specified storage location of the control unit, the storagelocation not being used in the overlaying.

This means, therefore, that the applications system calls for aswitching over of the pages by writing a message into a declared storagelocation of the control unit.

It may be provided that the switching over, that has occurred, of thememory pages by the software of the control unit is acknowledged, andthis may be done by the software of the control unit writing anacknowledgement identifier into a specified storage location, which isalso not used in the overlaying. In this context, the same or even adifferent storage location with respect to the acknowledgment identifierand the switching identifier may be involved. Thus, the control unitsoftware may return only one acknowledgment on the success of the pageswitching by writing a message into a storage location. The applicationssystem is able to interpret this response.

In an example embodiment, the first storage area of the control unitthat is overlaid by the second storage area is able to be changed duringthe operation of the control unit in that the control unit changes orcustomizes this first storage area by using an overlay configurationtable.

This means that it may be provided for the application system to changethe area of the memory that is being overlaid, during the operation.This broadened control of the page configuration by the applicationssystem is achieved by the control unit having an overlay configurationtable imparted to it.

It may also be provided, in this context, that the control unitprocesses the overlay configuration table in response to aninitialization process, that is, especially at the start of the controlunit, and thus, immediately upon the initialization, the first storagearea is overlaid by the second storage area, and the control unitsoftware is already processing the overlay configuration table duringbooting up. To do this, it may be provided that the overlayconfiguration table is stored in a storage area or in a storage locationwhich continues to hold the stored data even after shutdown of thesystem or in response to power loss, which is achievable especially by afloated battery, etc.

Example embodiments of the present invention are described below withreference to the figures illustrated in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the exemplary design of a measuring and/orapplications system, as it may be used according to example embodimentsof the present invention.

FIG. 2 illustrates the schematic design of a microcontroller todemonstrate the page switching method according to example embodimentsof the present invention.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary construction that is used for measuringsystems and/or application systems. In it, 100 shows a control unit inwhich at least one storage area is to be overlaid. The application unitor measuring unit, by which modifications, measurements and sequencechanges are to be carried out, is designated by 101. This unit,subsequently designated as application unit 101, is connected to controlunit 100 via additional hardware 102. In one special embodiment,hardware 102 can be made up of a conversion box 103 and emulationhardware 104. In this context, emulation hardware 104 may in particularbe an ETK, an emulation probe. Then, in conversion box 103, there takesplace the signal conversion between application unit 101 and controlunit 100 with respect to emulation hardware 104. The application unitmay particularly be a PC, laptop, etc. that is sold in the trade.

The partitioning of the hardware into a part outside and a part insidethe control unit is only exemplary, and is not intended in any way torestrict the subject matter of the present invention to the extent thata definite partitioning is absolutely prescribed. Thus, for one,conversion box 103 may be omitted and, besides the connection, forinstance, via the emulation probe with regard to component 104, it isalso possible to have a connection to another method, such as to a busconnection such as a CAN (controller area network), a USB (universalserial bus), a Flex Ray, TTCAN (time triggered controller area network)or even an XCP. That is why component 104 may be regarded as optionaland may be considered to be both within the control unit and outside ofit, and only connected to control unit 100. One example variant is theuse of emulation hardware such as an emulation probe, a conversion box103 for connecting application unit 101 to control unit 100. Additionalhardware 102 may, however, function only as signal conversion betweenapplication unit 101 and control unit 100. If application unit 101 andcontrol unit 100 have the possibility for direct communication, e.g. viaa CAN or a Flex Ray or even an USB, then in some cases additionalhardware 102 may be entirely omitted.

This means that example embodiments of the present invention, that is,the page switching method of the control unit according to exampleembodiments of the present invention, especially using overlayconfiguration tables, is applicable independently of the hardware, sothat generally any connection by which the memory of the microcontrollercan be changed, is suitable.

However, further on we shall specifically refer to the design havingemulation probe 104 and conversion box 103, in order to avoid anincomprehensible description by taking into account all possible designvariants. However, once having the knowledge of example embodiments ofthe present invention, it is no problem to transfer the method and thedevice according to example embodiments of the present invention to alarge number of different design variants of the hardware.

The hardware that is connected directly to the control unit, that is, inthis case, element 104, is called emulator probe below, and isabbreviated to ETK. This ETK is either incorporated in control unit 100or is applied outside the control unit and connected to it. Depending onthe type of the ETK, the connection may be made via the debug interfaceor to a parallel bus of the microcontroller. The control unit isexpediently in operation while the measuring and adjusting tasks arebeing carried out. The control unit is mostly installed in the vehicle,in this context, but it may also be tested outside of laboratoryconditions. In operation, the control unit assumes regulating tasks andcontrol tasks, such as, in a motor vehicle, with regard to enginecontrol or even brake control, transmission control, steering controlbasically the regulation and the control of any operating sequences,particularly in a motor vehicle, but also in machine tools in general,in automation or other applications.

In microcontroller 200 of control unit 100 there is also a read-writememory which is used to overlay data in another memory, for instance, aread-only memory, particularly a flash memory of the microcontroller.Thus, a first storage area of the microcontroller, especially aprogrammable read-only memory in the form of a flash memory, EEPROMmemory, PROM memory, but also an ROM is overlaid by a second storagearea. In the process, particularly the data in this first storage areaof the microcontroller are faded out by other data. Because of thisoverlaying of the first storage area by the second storage area, it ispossible, for instance, to measure parameters, visualize them on the PC,that is, application unit 101, and to change or customize them, whilethe control unit is fulfilling its operating task, especially in thevehicle.

With that, control unit 100 is able to be customized and optimized forthe application in question, especially for the vehicle in question,particularly in operation, e.g. while the vehicle is participating inroad traffic.

Now, FIG. 2 shows microcontroller 200 of control unit 100 which, besidesthe actual computing unit, that is, central processing unit CPU 201,also includes a first memory 203, a second memory 202, an interface 211as well as a memory management 204. First memory 203, second memory 202and memory management 204 are connected via first connection V1. CPU 201is connected to memory management 204 via a second connection V2, thatis, the CPU accesses the memories especially via memory management 204.Further units and components in the microcontroller, which are notrelevant to the method, are omitted here for the sake of improvedclarity. As was mentioned before, first memory 203 is, for instance, aflash memory, an EEPROM memory, an EPROM, a PROM, that is, in particulara programmed memory, it being also conceivable to have a read-onlymemory in the form of a ROM. This first memory 203 usually includes dataand/or programs which the microcontroller in the control unit uses forcarrying out the respective regulating task or control task. Read-writememory 202 may be developed as working memory, for instance, as avolatile memory, that is, as a RAM, but may also be developed, same asfirst memory 203, as a nonvolatile memory, that is, as described, as aprogrammable memory. In this case, however, particularly a RAM is usedfor memory 202. Interface 211 may be a serial as well as a parallelinterface, and as was described above, this may be the debug interface;but any other connection or rather interface is also possible at thislocation, just as was mentioned, a CAN, a USB; a Flex Ray, a TTCAN, anXCP, etc. With the aid interface 211, particularly the debug interface,it is possible for the measuring and/or application system, that is, theapplication unit or application system 101, to change the content ofsecond memory 202, that is, the read-write memory. Besides that, viathis interface 211, application system 101 is also able to customize andchange registers of the microcontroller, for example connection to theCPU. As was mentioned before, instead of a debug interface, any otherinterface, particularly a serial interface, may be used which offersaccess to the memory of the microcontroller.

The memory management also includes a memory management configurationregister 205, which may also be influenced via interface 111. Read-writememory 202 may be accommodated in the microcontroller itself, but couldalso be located outside in the control unit, especially on additionalhardware. Second memory 202 includes an area 210, in this instance, foraccommodating the overlay configuration tables ÜKT, a special storagelocation designated here as mailbox and numbered 206, as well as memorypages 1 and 2, designated as 208 and 209, between which switching overmay be performed and/or the overlaying may be switched on and off (EA),and which fade out an overlaid area in first memory 203, area 207depending on the switching by page switching PS. In this context it isalso possible that switching over between more than three pages couldtake place, for fading out overlaid area 207, so that security andpossibilities of variations are enhanced further. This means then thatthe application device is in a position to fade out certain areas,especially a certain first area in first memory 203, namely, overlaidarea 207 by overlaying memories, and thereby to adjust values while thecontrol unit is in operation. For reasons of security and for reasons ofvariability there may exist a plurality of pages 208 and 209, and inthis context, one of the pages may be omitted, since one may alsointerpret the original storage area as a memory page, between whichswitching may take place, in order, on the one hand, to increase themultiplicity of variants and, on the other hand, if necessary, to beable to return the control unit, or rather the systems controlled by thecontrol unit to a more secure state. In this instance, the applicationsystem calls for a switching of the pages, according to the presentinvention, by writing a message into a declared storage location, suchas mailbox 206 of the control unit. This means that a first storage area207 is overlaid by a second storage area, shown in this case by USL,which includes at least two memory pages 208 and 209. Switching overbetween the two pages 208 and 209 that overlay storage area 207, and/orthe switching on and off (EA) of the overlaying take place by pageswitching PS by memory management 204, to which access may be made byCPU 201, or even via interface 211 by the application system. Theswitching over then takes place automatically by control unit softwareor rather is executed by it. Because the control unit software carriesout or triggers the switching itself, it may be ensured that no accessis made to inconsistent data, since the current data are always present,and no intervention in this software takes place that generatesoverlapping inconsistencies. The calling for switching over by theapplication system is able to take place in particular by writing aswitching identifier UK into a specified storage location, e.g. mailbox206 of the control unit which is itself not used in the overlaying. Thecontrol unit software returns an acknowledgment concerning theoccurrence of the page switching, for example, by writing a message to astorage location. An acknowledgment identifier BK is thus writtenespecially into a specified storage location, for instance, also mailbox206 of the control unit, which is also not used in the overlaying. Thesame storage location as 206 in this case, but also different storagelocations, are able to be used for writing in switching identifier UK oracknowledgment identifier BK. The respective identifiers and messagesare then evaluated. Thus, the application system evaluates the responseof the control unit software, that is, acknowledgment identifier BK, andaccesses mailbox 206 for this, via interface 211.

One is able to obtain still greater flexibility, and it is consequentlyadvantageous for application system 101 if, during operation, theoverlaid storage area, that is, 207 in this case, is able to be changed,and one is completely free in the choice of the page that is to overlaythe respective storage area, in this context. In order to attain thisbroadened control of the page configuration by the applications system,the control unit has an overlay configuration table imparted to it. Suchan acknowledgment identifier configuration table ÜKT includesinstructions as to how the registers, that is, particularly the memorymanagement configuration register, but also other registers or thestorage locations, are to be modified by the control unit. Duringoperation of the control unit it is thereby possible to determine theconfiguration, that is, particularly to change the allocation of thepages to certain overlaid areas, and thus to use the overlaying memory,that is, second memory 202, very efficiently and flexibly, in order tofade out first memory 203 at the appropriate first storage areas, thefirst storage areas, same as the pages of second overlay storage areaUSL being simply able to be set flexibly, and in a customizable andchangeable manner. In this context, because of using the overlayconfiguration tables, the control unit software does not have to knowthe exact construction, the configuration and the utilization of theregisters, but it only processes one table, namely overlay configurationtable ÜKT, which includes all the required data for the modification ofthe storage areas and the storage locations, such as of mailbox 206.

CPU 201 is able to be triggered to process overlay configuration tablesÜKT, in storage area 210, by a message or an additional identifier. Thiscauses registers 205 of memory management 204 to be set appropriately.The result is, that a certain area of overlay memory USL fades out firstmemory 203, or rather, area 207 that is to be overlaid. Duringoperation, CPU 201 sees only the memory shown by memory management 204of microcontroller 200, which in this case simply corresponds to atleast one of the two pages 208 or 209 of overlay memory USL or to theoriginal storage area. The emulation hardware, that is, in this caseemulator probe ETK 104, controls microcontroller 200 with the aid ofinterface 211, in this context, especially the debug interface. It ispossible to modify the memory content of the read-write memory, that is,the RAM or second memory 202, and thus both to change the data and alsoto influence CPU 201. Using an appropriate program that is processed inCPU 201, it is possible that CPU 201 reacts during the writing onmailbox 206 by the emulation hardware, that is, the ETK, and that itprocesses the overlay configuration tables from area 210. The registersof the memory management, that is, the memory management configurationregisters 205 of microcontroller 200 are changed thereby. This, in turn,has the result that another area of the first memory, that is, inparticular, of read-only memory 203, is faded out by read-write memory202, especially by overlay area USL. In addition, by the use of theoverlay configuration tables in storage area 210, it is also possible tochange the size and the position of the area that is faded out, that is,of overlaid area 207, or, however, to switch off the overlaying. This issimply done, as was mentioned before, by processing the instructions inthe overlay configuration table. In that table, it is specificallydescribed how registers 205 are to be modified, and, as a function ofthese modifications, the changes in the size and position of theoverlaid area that were described, as well as the size, position andwhich page of the overlaid area, are able to be adjusted duringoperation. Thus, for example, the starting and the end address of theoverlaid area are shown, and so are the starting address and the endaddress of the overlaid area in the ÜKT. The size and the position ofthe respective storage areas are also able to be shown by using pointersin the ÜKT. The registers in the memory management are then simplyfilled with these pointers and/or the pointer addresses, or rather thestarting addresses or end addresses for the respective areas, namely,the first and/or second storage area, which is to say, the overlaid areaas well as the overlaying area. On the one hand, this gives applicationsystem 101 an extremely great measure of flexibility with respect to theconfiguration, and besides that, data inconsistencies are avoided sincethe control unit software itself is still carrying out the pageswitching, and also accesses the respective addresses and addresspointers.

For the application of a control unit, in many cases it is meaningful tostart by using an active overlay memory. That is, in the initializationphase, for instance, during booting up or even after a reset, it makessense just to access overlay memory USL and corresponding page 208 or209, and not first to initialize using overlaid area 207. With that, itis then possible to carry out the application directly from the bootingup of the control unit. To accomplish this, a direct allocation of thecontrol unit software to the overlay configuration tables in 210 cantake place, so that the control unit software at initialization, thatis, particularly at booting up, immediately processes the overlayconfiguration tables and thus starts at once with the overlay area, thatis pages 208 and 209 from USL, instead of overlaid area 207. To do this,it is meaningful not to put the overlay configuration table in volatilestorage. This can also take place by using a battery-backed memory orstorage area, in which overlay configuration tables ÜKT are stored sothat they are immediately available upon initialization. These overlayconfiguration tables do not first have to be imported into the controlunit by application system 101, but are present there directly and arethen particularly able to be used directly upon initialization. But evenwhen ÜTK is not used directly upon initialization, it is meaningful tostore it in a nonvolatile memory in the control unit, so that first ofall no intervention of application system 101 has to take place withinthe scope of page switching.

In this context, each individual one of these pages may be made up of aplurality of regions, for each region one register of the memorymanagement of microcontroller 200 being responsible respectively. Thatbeing the case, under certain circumstances it would not be possible tocarry out the page switching all at once, so that the switching wouldoccur successively which, as in the related art, could also lead toinconsistent data records. However, because the control unit softwareitself carries out the writing of registers 205 in the method accordingto example embodiments of the present invention, the page switching isable to take place at a time when the control unit software isespecially not accessing the memories. This ensures that there is nooverlap during memory access, and consequently, that the control unitsoftware does not access inconsistent intermediate readings of the data.As was mentioned before, besides the design using two pages 208 and 209,any other number of pages would also be possible.

In particular, just one page is possible, the second configuration beingthen formed by the initial state of registers 205.

Now, the page switching method according to example embodiments of thepresent invention in a control unit, by overlay configuration tablesparticularly has the advantage compared to the related art that it iscompletely genetic, and the control unit software does not have to becustomized, but is able to be used unchanged for different memorypartitionings. When it comes to hardware changes, it is also possible toleave the measuring system and the application system unchanged, andonly to customize the overlay configuration tables appropriately.

The method introduced is also demonstrable in the form of a computerprogram having program code, and made to be executed on a system asdescribed in FIG. 1, which includes a device according to an exampleembodiment of the present invention. In this context, the computerprogram is also able to be stored on a data carrier that iscomputer-readable, for instance, a CD-ROM, a disk, a DVD, an EEPROM, anEPROM, a flash memory, a memory card, a chip card, a PROM, a ROM, a RAMor other storage media which are able to be read in any form by acomputer. The representation as a computer program represents only aspecial form and is based on the same technical principles of exampleembodiments of the present invention.

What is claimed is:
 1. A method for switching over in a memory for acontrol unit, a first storage area in the control unit being overlaid bya second storage area, the second storage area including at least twomemory pages, each memory page configured to overlay the first storagearea, comprising: performing, by software of the control unit: (i)switching over between an original non-overlaid memory configuration andan overlaid configuration in which one of the two memory pages of thesecond storage area overlays the first storage area, and (ii) switchingover between overlaying the first storage area using a first one of thememory pages of the second storage area and overlaying the first storagearea using a second one of the memory pages of the second storage area;in the non-overlaid memory configuration, read-accessing the firststorage area using the control unit; and in the overlaid configuration,read-accessing the overlaying memory page in place of the first storagearea, using the control unit.
 2. The method according to claim 1,wherein at least one of (a) the switching over between the originalnon-overlaid memory configuration and the overlaid configuration and (b)the switching over between the overlaying of the first storage areausing the first one of the memory pages of the second storage area andthe overlaying of the first storage area using the second one of thememory pages of the second storage area is called for by an applicationsystem.
 3. The method according to claim 2, wherein the applicationsystem calls for at least one of (a) the switching over between theoriginal non-overlaid memory configuration and the overlaidconfiguration and (b) the switching over between the overlaying of thefirst storage area using the first one of the memory pages of the secondstorage area and the overlaying of the first storage area using thesecond one of the memory pages of the second storage area in that aswitching identifier is written into a specified storage location of thecontrol unit which is not used in the overlaying.
 4. The methodaccording to claim 1, wherein the software of the control unitacknowledges that at least one of (a) the switching over between theoriginal non-overlaid memory configuration and the overlaidconfiguration and (b) the switching over between the overlaying of thefirst storage area using the first one of the memory pages of the secondstorage area and the overlaying of the first storage area using thesecond one of the memory pages of the second storage area has takenplace.
 5. The method according to claim 4, wherein the software of thecontrol unit acknowledges at least one of (a) the switching over betweenthe original non-overlaid memory configuration and the overlaidconfiguration and (b) the switching over between the overlaying of thefirst storage area using the first one of the memory pages of the secondstorage area and the overlaying of the first storage area using thesecond one of the memory pages of the second storage area in that anacknowledgment identifier is written into a specified storage locationof the control unit which is not used in the overlaying.
 6. The methodaccording to claim 1, wherein the first storage area, which is overlaid,is changeable during operation of the control unit in that the controlunit changes the first storage area with the aid of an overlayconfiguration table.
 7. The method according to claim 6, wherein theoverlay configuration table is written into the control unit by anapplication system and is changed during the operation.
 8. The methodaccording to claim 6, wherein in response to an initialization process,the control unit processes the overlay configuration table, andimmediately upon the initialization, the first storage area is overlaidby the second storage area.
 9. The method according to claim 6, whereinswitching over is performed by setting values of registers in a memorymanagement unit based on the overlay configuration table, the registervalues indicating which one of (i) the first storage area and (ii) atleast one of the two memory pages in the second storage area, isaccessible by the control unit.
 10. The method according to claim 1,further comprising: updating content of the first storage area afterswitching to the overlaid configuration.
 11. The method according toclaim 10, further comprising: performing, by the software of the controlunit, a switch back to the non-overlaid configuration after the contentof the first storage area has been updated.
 12. A device for switchingover in a memory for a control unit, comprising: a first storage area inthe control unit; a second storage area, the first storage area beingoverlaid by the second storage area, the second storage area includingat least two memory pages; wherein the device is configured such thateach of the memory pages is able to overlay the first storage area, andwherein (i) switching over between an original non-overlaid memoryconfiguration and an overlaid configuration in which one of the twomemory pages of the second storage area overlays the first storage area,and (ii) switching over between overlaying the first storage area usinga first one of the memory pages of the second storage area andoverlaying the first storage area using a second one of the memory pagesof the second storage area are performed by software of the controlunit; wherein the control unit is configured to perform read-accesses tothe first storage area in the non-overlaid memory configuration; andwherein the control unit is configured to perform read-accesses to theoverlaying memory page in place of the first storage area in theoverlaid configuration.
 13. The device according to claim 12, wherein atleast one storage location is provided which is not used in theoverlaying, and into which a switching identifier is written to call forthe switching over.
 14. The device according to claim 12, wherein atleast one storage location is provided which is not used in theoverlaying, and into which an acknowledgment identifier is written toacknowledge the switching over.
 15. The device according to claim 12,wherein an overlay configuration table is written into the control unitby an application system, and the device is configured such that theoverlay configuration table is able to be changed during operation. 16.The device according to claim 15, wherein the device is configured suchthat, in response to an initialization process, the control unitprocesses the overlay configuration table, and, immediately upon theinitialization, the first storage area is overlaid by the second storagearea.
 17. The device according to claim 12, wherein a storage area isprovided for an overlay configuration table, and the device isconfigured such that the first storage area which is overlaid is able tobe changed during operation of the control unit in that the control unitchanges the first storage area with the aid of the overlay configurationtable.
 18. The device according to claim 17, wherein the storage areahaving the overlay configuration table is configured such that evenafter power supply of the device is switched off, the overlayconfiguration table remains intact.
 19. A non-transitorycomputer-readable storage medium encoded with instructions configured tobe executed by a processor, the instructions which, when executed by theprocessor, cause the performance of a method for switching over in amemory for a control unit, a first storage area in the control unitbeing overlaid by a second storage area, the second storage areaincluding at least two memory pages, each memory page configured tooverlay the first storage area, the method including: performing bysoftware of the control unit: (i) switching over between an originalnon-overlaid memory configuration and an overlaid configuration in whichone of the two memory pages of the second storage area overlays thefirst storage area, and (ii) switching over between overlaying the firststorage area using a first one of the memory pages of the second storagearea and overlaying the first storage area using a second one of thememory pages of the second storage area; in the non-overlaid memoryconfiguration, read-accessing the first storage area using the controlunit; and in the overlaid configuration, read-accessing the overlayingmemory page in place of the first storage area, using the control unit.